1. Field of the Invention
The present invention relates to a keyway machining path creating device for wire electric discharge machines.
2. Description of the Related Art
A keyway is machined in a side surface of a round hole formed in a workpiece using a wire electric discharge machine.
Japanese Patent Application Laid-Open No. 8-153132 discloses a CAD/CAM apparatus capable of automatically performing plotting only by selecting a defined hole and inputting parameters to thereby generate keyway machining data and NC data. The CAD/CAM apparatus diagnoses keyway parameters including a hole diameter and a keyway depth using a keyway database registered in advance.
In order to create a machining path using a keyway machining path creating device for wire electric discharge machines, a user designates the shape (a keyway width, a keyway depth, and the like) of a keyway to be machined and designates the diameter and the center position of a round hole machined in a workpiece. Here, the following two methods are generally used to designate a keyway depth.
According to Method 1, the keyway depth is designated by a cut depth (t) which is a distance from a hole side surface at a keyway width center to a keyway bottom.
According to Method 2, the keyway depth is designated by a measured depth (1) which is a distance from a hole side surface on the side opposite a keyway width center to a keyway bottom.
FIG. 1 illustrates a keyway depth as the distance t (cut depth) from a hole side surface at a keyway width center to a keyway bottom. On the other hand, FIG. 2 illustrates a keyway depth as the distance 1 (measured depth) which is the distance from a hole side surface on the side opposite a keyway width center to a keyway bottom. In this manner, machining dimensions of a keyway are generally expressed by the method illustrated in FIG. 1 or 2. An operator creates a keyway machining NC program using a keyway machining path creating device for wire electric discharge machines by referring to the dimensions illustrated in FIG. 1 or 2.
FIG. 3 is an example of a display screen for creating a keyway machining program. Moreover, FIG. 4 is an example of a macro program for creating a keyway machining path. An operator inputs the keyway machining dimensions illustrated in FIG. 3 to a machining path creating device prepared as a macro program or screen to create a keyway machining NC program.
When creating a keyway machining NC program, an operator has to understand whether the value “keyway depth” input to the keyway machining path creating device is the “cut depth t” or the “measured depth l”.
For example, when a keyway depth has to be designated by such a “cut depth t” as illustrated in FIG. 1 on a keyway machining program creation screen of FIG. 3 whereas the keyway depth is designated by such a “measured depth l” as illustrated in FIG. 2 on a machining drawing, the operator has to input a value obtained by subtracting the hole diameter d from the measured depth l to the keyway machining path creating device as the “keyway depth”.
Thus, there is a possibility that the operator miscalculates the keyway depth or input wrong dimensions (for example, an operator may erroneously inputs the “measured depth l” on the keyway machining program creation screen of FIG. 3, instead of the “keyway depth (t)”). Such an input error results in the inability to machine a keyway in correct dimensions.
As a method for solving this problem, a method of allowing an operator to input the dimensions of both the “cut depth t” and the “measured depth l” to the machining path creating device may be used. However, this method increases the number of input items, which thus increases the burden on the operator. Moreover, in general, since only one of the “cut depth t” and the “measured depth l” appears in a machining drawing, the operator has to perform the calculation and may make miscalculations similarly to the above-described problem.
As another solving method, the machining path creating device may have a function of switching an input keyway depth to the “cut depth t” or the “measured depth l”. In this case, the operator uses a machining path creating device which is switched according to a machining drawing. However, the operator may make a mistake in the switching, and in such a case, it is not possible to machine a keyway in correct dimensions.
In view of the above, the operator has to determine whether the method of designating a keyway depth in the machining path creating device used is based on Method 1 or 2 described above and then designates appropriate data. For example, when the keyway depth is designated by a “measured depth” in a machining drawing whereas the keyway depth is designated by a “cut depth” in a keyway machining path creating device used, the operator has to convert the measured depth designated in the machining drawing to a cut depth (subtract a diameter of a round hole from the designated measured depth to calculate a cut depth) and designate the calculated keyway depth (cut depth) to the keyway machining path creating device. Thus, the planning operation incurs a lot of labor and time and the operator may designate a wrong keyway depth.